Take advantage of the current libc sizeof(FILE) breakage (sF[]) and
try a hopefully more robust stdin/stdout/stderr. This costs an indirect
pointer fetch, but saves us from changes in 'FILE'. The stdin stuff
is there to not pollute application name space if the application does
not use <stdio.h> and also in case something depended on the current
behavior where stdin etc was a #define.

Reviewed by: eischen, dillon